On Tue, 13 May 1997 11:26:48 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>On page 18 of Care and Feeding of Power Grid Tubes (Varian):
>
>"a thoriated filament will produce a specific PEAK emission of about
>70 to 100 mA per watt of filament heating power. This is normally 5
>to 10 mA of CW plate current per watt of filament power."
>
>The specific peak emission is what is applicable to the parasitic
>"theories". That is the absolute maximum emission current available
>under any bias voltage condition.
No Tom, that is only the peak "permissable" current and has absolutely no
bearing on fault condition parameters. You keep dancing all around the
subject but refuse to stay on track....you too Rich.
In a catastrophic failure mode the current can be whatever it takes to
cause the damage. A VHF parasitic can approach 20-30KV or more, even in a
simple 811A circuit. It depends largely upon the unloaded Q of the
tank circuit since the load IS NOT absorbing ANY parasitic energy.
Tom, you seem to enjoy references to UFO's and space.
Permit me to use the Challenger as an example.... Lots of energy normally
under control but suddenly dissipated in an instant. I use that example
since I watched that catastrophe and Christa McAuliffe was a local NH
teacher...kinda hit us "locals" a bit hard.
>Other tube design and engineering books agree with this, the highest
>number I've found is 125 mA per watt.
>
>The CW emission capability of a metal oxide cathode tube is typically
>200-300 mA per watt of heater power, about 30 times the CW emission
>of a thoriated tungsten tube.
>
>I may be confused, but I thought we were discussing 811's and
>3-500's.
We are all drifting Tom....I am trying to stick to the 811A ONLY for now.
We can take up 3-500Z's, 572B's and tubes with handles later. I would
prefer to stick to one subject at a time so I can keep you and Rich at
least partially focused.
That way you cant confuse the issue by throwing in graphite plate gassing
in the middle of a Tantalum plate discussion as a way to dance around.
No personal offense meant....I'm just a one subject New Englander.
73....Carl KM1H
>73, Tom W8JI
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